@Justin Xu,
Justin, I have a question... have you been able to get to the threads you already started, to read the replies you have already gotten? There has been a lot of duplication. (You ask something, it's answered, then you ask again.)
At any rate, yes, you are correct about generous referring to "large" or "roomy" here.
Antebellum literally means "before the war," (latin), it usually is used to refer to the period before the American Civil War. That time period is now far enough in the past that most people now can't readily think of what "antebellum elegance" would mean, but I seem to remember this ad was from the 1920's or 1930's, in which case that period would be more fresh in people's memories.